Starting device for electric motors.



No. 809,878. PATENTED JAN. 9, 1906.

H. B. WILSON.

STARTING DEVICE FOR ELECTRIC MOTORS.

APPLICATION FILED MAR.10, 1904.

SELF-REDUCING RES/S TA NCE.

Wfimesses: Inventor.

% Howard BWiison UNITED STATES PATENT OFFICE.

HOWARD B. WILSON, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

STARTING: DEVICE FOR ELEGTREG NEOTORS= Specification of Letters Patent.

Patented Jan. 9, 1906.

Application filed March 10, 1904. Serial No. 197,484.:

To aZZ whom ,it may concern.-

Be it known that I, HOWARD B. Wr-Lson, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Starting Devices for Electric Motors, of which the following is a specification.

My invention relates to starting devices for electric motors, and refers particularly to starting devices comprising an automatic self-reducing resistance.

Certain substances possess such a high negative temperature coefficient that they are suitable for use as starting resistances for-electric motors and are known as selfreducing resistances. Such substances, of Which magnetite is one, automatically reduce their resistance as they are heated by the flow of current and While possessing a high initial resistance offer only a very low final resistance when heated by the current. Although this final resistance is very low, nevertheless it produces a certain loss of energy if left in circuit, and, moreover, it left in circuit it remains heated, so that if the current were suddenly interrupted and again applied the resistance would be too low to serve as a proper starting resistance for the motor.

The object of my invention is to provide means for automatically cutting out the resistance when it is reduced to a certain value.

I thus prevent a loss of energy in the resistance while the motor is running and also give the resistance a chance to cool, so that when the motor-circuit is interrupted it will immediately be in proper condition to act as a starting resistance for the motor.

My invention will be best understood from the accompanying drawing, in which M represents a motor having an armature a and a field I have indicated in the draw ing a shunt-wound direct-current motor; but it will be understood that my invention is not limited to this particular form. of motor. a

R represents a self reducing resistance,- such as magnetite, which at starting is connected in series with the motor-armature a.

S represents a switch member pivoted on the support A and operated by the handle H. The handle H is connected to the switch member S by the link L in such manner that when the handle is pushed down the switch member S is closed and brought into engagement with the stationary contact S. Switch member S carries the auxiliary carbon contact O, arranged to engage the stationary carbon contact C.

B is a no-load release-magnet of the ordi nary type and is connected across the line or the motor-field, as shown.

B is the armature for magnet B and when magnet B is denergized is heldin the position shown in the drawing by the tension-spring b.

' D is a second magnet having the armature D" pivoted at (Z. Armature D carries at either end a flexible contact E and E. Contact E is arranged to be engaged by the switch member S as the switch is closed, and the contact E is arranged to engage the contacts F F when armature Dis rotated on its pivot, but is held out of engagement with these contacts by springewhen the motor-circuit is open and by spring e, in connection with magnet D, when magnet D is energized; Contacts F F are connected across the terminals of the self reducing resistance R. Magnet D is also connected across these terminals.

The operation is as follows: When handle H and armature B are pushed down, switch member S is moved upward until the auxiliary contacts CC are inengagement. A circuit is then completed from the line-wire 2 through switch member S, through the resistance B, through the armature a and to line-wire l. A second circuit is completed through the field f of the motor. The motor accordingly starts with resistance R in series with the armature. Magnet B, which is in shunt to field f, is energized and holds down its armature against the tension of spring I). Magnet D, which is connected in shunt to resistance R, is also energized and holds down its armature D. As the downward motion of handle H is continued switch member S engages flexible flat spring E, which bends and is placed under tension by the further movement of switch S, since armature D is locked in position by the magnet D. Switch member S is now fully closed in engagement with contact S. This condition of circuits continues as long as the self-reducing resistance R maintains an appreciable resistance. The resistance is steadily decreasing as it is heating up by the flow of current, and consequently the volta e across the terminals of magnet D is steadi y decreasing. When this voltage drops to a predetermined amount, magnet D is no longer able to hold its armature D against the tension or" the spring E, and armature D consequently rotates on its pivot 61 against the tension of sprin '6, bringing contact E into engagement Wil contact F, thereby short-circuiting the resistance R. Resistance R is consequently cut out of circuit, and all loss of energy in the resistance while the motor is running is prevented.

Furthermore, this resistance no longer car ries any current, and consequently has an opportunity to cool down, so as to be in the proper condition to act as a starting resistance if the circuit of the motor is interrupted and immediately closed. If the supply-current fails, magnet B releases its armature B, which is drawn up by spring D, raising handle H, opening switch S, and restoring the circuits totheir starting conditions.

it do not desire to limit myself to the particular construction and arrangement of parts here shown, since changes which do not depart from the spirit of my invention and which are within the scope of the appended claims will be obvious to those skilled in the art.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

1. In combination, an electric motor, and means for starting the same comprising a self-reducing resistance connected in the motor-circuit, and automatic means for cutting said resistance out of circuit when its ohmic value is'reduced to a predetermined amount.

2. In combination, an electric motor, and

means for starting the same comprising a self-reducing resistance connected in the motor-circuit, a switch-contact arranged to out said resistance out of circuit, and automatic means for actuating said switch-contact when the potential drop in said resistance falls to a predetermined amount.

3. In combination, an electric motor, and means for starting the same comprising a selfreducing resistance connected in the motorcircuit, a magnet-winding connected in a circuit in which the current varies when the ohmic value of said resistance changes, and a switch-contact controlled by said magnetwinding and arranged to cut said resistance out of circuit. I

4. The combination of an electric motor, and means for starting the same comprising a self-reducing resistance connected in the motor-circuit, a magnet-winding connected in a circuit in which the current decreases when the ohmic value of said resistance decreases,

and a switch-contact controlled by said winding and arranged to cut said resistance out of circuit. I

5. The combination of an electric motor, and means for starting the same comprising a self-reducing resistance connected in the motor-circuit, a magnet-winding connected in shunt to said resistance, and a switch-contact controlled by said magnet-winding and arranged to short-circuit said resistance when the potential drop in said resistance falls to a predetermined value.

6. The combination of an electric motor, and means for starting the same comprising a self-reducing resistance connected in the motor-circuit, a switch-contact adapted to shortcircuit. said resistance, means tending to move said contact to short-circuit said resist-- ance, and a magnet-winding connected in shunt to said resistance and adapted to restrain said switch-contact until the potential drop in said resistance falls to a predetermined value.

7 lln a motor-starting device, a self-reducing resistance, a switch contact arranged when moved to short-circuit said resistance, a switch adapted to close the motor-circuit and arranged to put a strain upon said contact, and a magnet connected in shunt to said resistance and adapted to restrain said contact until the potential drop in said resistance falls to a predetermined value.

8. In combination, an electric motor, and means for starting the same comprising a magnetite resistance connected in the motorcircuit, and automatic means for short circuitin said resistance when the otential drop t erein falls to a predetermined value.

9. In combination, an electric motor, and means for starting the same comprising a magnetite resistance connected in the motorcircuit, a switch-contact arranged to out said resistance out of circuit, and automatic means for actuating said switch-contact when the resistance of said magnetite falls-toe predetermined value.

10. A motor-starting device comprising a resistance body having a negative temperature coeflicient, means for including it in circuit on starting, and automatic means for cutting it out after the motor has started.

11. A. motor-starting device comprising a resistance unit of conductin -oxid, a switch, and means for cutting out t e unit when it has been heated a determinate de ree.

12. In a starting-switch for e ectric motors, a movable switch member adapted to establish when moved the running connections for'the motor, a magnet-winding adapted to restrain said member at starting, and means independent of the speed of the motor for impressing an automatically-decreasing voltage on said magnet.

13. in a starting-switch for electric motors, a movable switch member adapted to establish when moved the running connections for the motor, a ma net-Winding adapt- In witness whereof I have hereunto set my ed to resgtirain slaid nierfi er atdstfiriing, and hand this 8th daypf March, 1904.

means in epen ent 0 t e spee o t 1e motor *1 T for impressing an automatically-decreasing HOWARD WILbQI 5 voltage on said magnet, said switch member Witnesses:

being arran ed to short-circuit said magnet BENJAMIN B. HULL,

when move to running position. HELEN ORFORD. 

